The present invention relates to an automatic transmission which may be installed to automotive vehicles.
Conventionally, according to an automatic transmission equipped with a torque converter and a transmission mechanism, oil which is sucked by an oil pump from an oil pan disposed at a lower portion of the transmission mechanism, as operational oil, is supplied to frictional elements and the torque converter which constitute the transmission mechanism via a control valve unit. Further, the operational oil discharged from the torque converter is cooled or heated at a heat exchanger and then supplied to various portions of the transmission mechanism as lubricating oil for bearings and frictional plates of the transmission mechanism.
Herein, the lubricating oil discharged from the torque converter is supplied not only from a torque-converter side (hereinafter, referred to as “front side”), but also from an anti-torque-converter side (hereinafter, referred to as “rear side”) in the transmission mechanism. Thus, the lubricating oil can be sufficiently supplied to an whole part of the transmission mechanism.
Moreover, in order to supply the lubricating oil to the rear side, a lubricating oil passage which extends toward the rear side from the front side is formed in a wall of a transmission case which stores the transmission mechanism, like an automatic transmission disclosed in U.S. Patent Application Publication No. 2007/0131053 A1, for example.
That is, according to the automatic transmission disclosed in the above-described publication, the lubricating oil passage has an introduction port of the lubricating oil discharged from the torque converter which is formed at a wall portion of the transmission case on the front side. Further, this lubricating oil passage extends, in a peripheral wall portion, toward a wall portion of the transmission case on the rear side from the above-described introduction port, and further extends, in the wall portion on the rear side, from a connection portion to the peripheral wall portion toward a center portion of the wall portion on the rear side. A support portion to support a power transmission shaft which is disposed at a center portion of the transmission mechanism is formed at the center portion of the wall portion on the rear side, and the above-described oil passage connects to an oil passage formed in the power transmission shaft via the above-described support portion. This oil passage in the power transmission shaft has plural holes to supply the lubricating oil to the transmission mechanism which is disposed at the periphery of the power transmission shaft. Thus, the lubricating oil discharged from the torque converter flows into the passage in the power transmission shaft via the passage passing through the wall portion on the front side, the peripheral wall portion, the wall portion on the rear side, and the support portion of the power transmission shaft of the transmission case, and then is supplied to the transmission mechanism from the rear side via the plural holds.
The oil passage to supply the lubricating oil discharged from the torque converter disposed on the front side to the rear side may be formed inside the power transmission shaft at the central portion of the transmission mechanism instead of the above-described structure. Herein, in case another passage to supply the control pressure of the frictional elements of the automatic transmission is formed inside the power transmission shaft, or in case the power transmission shaft is comprised of a front shaft and a rear shaft which are spilt from each other, a single oil passage which extends from the front side to the rear side may not be formed. Accordingly, it may be necessary to form the oil passage by using the transmission case like the automatic transmission disclosed in the above-described automatic transmission.
However, in order to form the oil passage extending a front-side end portion to a rear-side end portion in the wall of the transmission case, lots of processing using tools, such as a long and thin drill, may be required. Therefore, the processing costs of the oil passage, thus the manufacturing costs of the automatic transmission would increase.